The present invention relates generally to the field of electrolytic plating compositions. In particular, the present invention relates to the field of copper electroplating compositions.
Methods for electroplating articles with metal coatings generally involve passing a current between two electrodes in a plating solution where one of the electrodes is the article to be plated. A typical acid copper plating solution comprises dissolved copper (usually copper sulfate), an acid electrolyte such as sulfuric acid in an amount sufficient to impart conductivity to the bath, and proprietary additives to improve the uniformity of the plating and the quality of the metal deposit. Such additives include brighteners, levelers, surfactants, suppressors, and the like.
Electrolytic copper plating solutions are used for many industrial applications. For example, they are used in the automotive industry to deposit base layers for subsequently applied decorative and corrosion protective coatings. They are also used in the electronics industry, particularly for the fabrication of printed circuit boards and semiconductors. For circuit board fabrication, copper is electroplated over selected portions of the surface of a printed circuit board and onto the walls of through holes passing between the surfaces of the circuit board base material. The walls of a through hole are first metallized to provide conductivity between the board's circuit layers. For semiconductor fabrication, copper is electroplated over the surface of a wafer containing a variety of features such as vias, trenches or a combination thereof. The vias and trenches are metallized to provide conductivity between various layers of the semiconductor device.
It is well known in certain areas of plating, such as in electroplating of printed circuit boards, that the use of brighteners and/or levelers in the electroplating bath can be crucial in achieving a uniform metal deposit on a substrate surface. Plating a substrate having irregular topography can pose particular difficulties. During electroplating a voltage drop variation typically will exist along an irregular surface which can result in an uneven metal deposit. Plating irregularities are exacerbated where the voltage drop variation is relatively extreme, i.e., where the surface irregularity is substantial. As a result, a thicker metal deposit, termed overplating, is observed over such surface irregularities. Consequently, high quality metal plating (e.g., a metal layer or plate of substantially uniform thickness) is frequently a challenging step in the manufacture of electronic devices.
Leveling agents are often used in copper plating baths to provide substantially uniform, or level, copper layers. For example, U.S. Pat. No. 4,038,161 (Eckles et al.) discloses a method of producing level copper deposits by electroplating copper from a copper plating bath containing at least one organic leveling compound obtained by reacting one or more epihalohydrins with one or more nitrogen containing compounds selected from certain substituted pyridines, quinolione or aminoquinoline, isoquinoline or benzimidazole. Reaction products of imidazoles are not disclosed. This patent fails to disclose the copper plating of small features in substrates used in the manufacture of integrated circuits.
The use of leveling agents in semiconductor manufacture is known but such agents are known to provide poor fill performance of small features, such as vias and trenches. For example, known leveling agents that have been used in semiconductor manufacture form substantially planar surfaces, however, they also form a substantial number of voids in the vias or trenches. Such voids can cause electrical open circuits in the semiconductor. As the geometries of electronic devices get smaller, the difficulty of plating a uniform copper layer while completely filling the smaller features becomes more difficult.
One proposed solution is that found in U.S. Pat. No. 6,024,857 (Reid) which discloses the use of certain leveling agents in the copper electroplating of wafers. In this patent, the leveling agents are selected such that they consist essentially of molecules having a size at least equal to the width of the feature to be plated. Such leveling agents are macromolecules, having molecular weights of from 200,000 to 10,000,000. Such an approach is problematic when features of different sizes are present in the same substrate. Also, such leveling agents are so large that they are removed from the plating baths during normal filtration processes to remove particulates.
Thus, there is a need in the art for leveling agents for use in semiconductor manufacture that do not form voids, show reduced overplating and are useful for plating substrates having different sized features.